There are available a number of fluid operated, expansible shafts. In most, buttons in the periphery of the shaft are forced radially outward into engagement with a surrounding core when fluid under pressure is supplied to the shaft interior. These devices are subject to several problems, including loss of holding force due to leakage, clogging caused by fiber particles and other foreign materials, and inability without expensive couplings to add make-up air under leakage conditions.